An animal model for the chronic study of ventricular repolarisation and refractory period.

We have developed a simple model permitting stable, chronic measurements of ventricular repolarisation and refractory period to be made in conscious, unsedated, unrestrained animals. The model utilises the ventricular paced evoked response, recorded from permanent pacemaker electrodes implanted into the right ventricle of New Zealand White rabbits. After a "bedding in" period of 18-21 d, measured variables are stable for long periods; the stimulus to T wave interval of the evoked response remains stable up to at least 150 d after electrode insertion. The principal advantage of the model lies in the control of heart rate by pacing, eliminating the requirement for unreliable methods of correction of repolarisation data for sinus rate. Surgical techniques are straightforward. The model can also be used for studies involving recordings of the intrinsic (non-paced) intracardiac electrogram, as the quality of the signal obtained is consistently superior to standard methods of recording the electrocardiogram in animals. The stimulus-T interval of the paced evoked response has been found to correlate significantly (r = 0.96) with action potential duration measured by transmembrane microelectrode recordings in the isolated, arterially perfused interventricular septum.